基于转换机制的过渡金属氧化物与硫化物复合材料的锂电性能研究

【作者】 李晨；

【导师】 李山东；

【作者基本信息】 青岛大学 ， 材料工程（专业学位）， 2018， 硕士

【摘要】 近年来,便携式电子产品及新能源交通工具的飞速发展对其作为动力之源的锂离子电池提出了更高的要求,而目前商用石墨负极材料由于比容量较低已经无法满足现代产品的需求,因此,研制高性能的电池正负极材料迫在眉睫。其中,过渡金属氧化物及硫化物由于具有比容量高、资源丰富、环保等优点,成为最可能取代商用石墨的锂离子电池负极材料之一。然而,由于在充放电过程中,过渡金属氧化物及硫化物会发生转化反应致使其体积变化较大,容量衰减较快,进而导致其循环稳定性较差。而且其导电性相对较差使其倍率性能有待提高。因此,本论文主要围绕制备高性能的过渡金属氧化物、硫化物负极材料以及提高其能量密度来展开工作。本论文在铁酸镍/石墨烯复合材料体系中同时探究了石墨烯的复合比例和粘接剂对电极材料电化学性能的影响,为提高锂电池的性能提供了一种新颖的策略。本论文采用水热法与热退火工艺制备出粒径为20nm的铁酸镍纳米颗粒均匀地分布于石墨烯上,即铁酸镍/石墨烯复合材料。当铁酸镍/石墨烯复合材料以羧甲基纤维素钠为粘接剂用作锂离子电池负极材料时,其展现出了优异的储锂性能:包括较高的可逆容量、良好的循环性能以及优异的倍率性能。而在相同复合比例、相同测试条件下,以聚偏氟乙烯为粘接剂的铁酸镍/石墨烯复合材料却呈现出了急剧的容量衰减。所以,在合适的石墨烯复合比例与匹配的粘接剂的协同作用下,铁酸镍/石墨烯复合材料有望成为新型的锂离子电池负极材料。与相应的金属氧化物相比,金属硫化物在同时具有氧化物优点的基础上相较于氧化物拥有有更好的导电性以及更小的体积变化。在众多的硫化物负极材料中,硫化钴由于具有储量丰富、导电性好、理论比容量也比较高等优点,成为有应用前途的锂离子电池负极材料。不过,其在电化学反应过程中也存在一定程度的体积膨胀效应,这会导致电极材料的粉化与破裂。因此,我们拟通过优化材料的结构以及与碳复合等方式来解决上述问题。本文针对硫化钴材料的特点,通过溶剂热法和金属有机物骨架模板法,制备了特定形貌和尺寸的硫化钴材料,以此作为锂离子电池电极材料,系统探讨并研究了其电化学性能。更多还原

【Abstract】 In the past few decades,the portable electronic devices（laptops,mobile phones,cameras）and new energy vehicles have a great development.But the commercial graphite anode material cannot meet the needs of electronic devices.Therefore,it is urgent to exploit new anode materials for the high performance lithium ion batteries.Transition metal oxides and sulfides are considered to be the most possible anode material for the next generation of commercial lithium ion batteries,which have high specific capacity,non-pollution and rich resources.Also,transition metal oxides and sulfides have disadvantages of capacity decaying while cycling and poor conductivity.Therefore,this paper focuses mainly on preparing good chemical performance transition metal oxide and sulfide anode materials for lithium ion batteries.The combination of carbon compositing and the proper choice of binders in one system offer an effective strategy for improving electrode performance for lithium ion batteries（LIBs）.Here,we focus on the optimization of reduced graphene oxide content in NiFe₂O₄/reduced graphene oxide（abbreviated to NiFe₂O₄/rGO）composites and the proper choice of binders to enhance the cycling stability of the NiFe₂O₄ electrode.The NiFe₂O₄/rGO composites were fabricated by a hydrothermal-annealing method,in which the mean size of spinel NiFe₂O₄ nanoparticles was approximately 20 nm.When tested as anode materials for LIBs,the NiFe₂O₄/rGO electrodes with carboxymethylcellulose（CMC）binder exhibited excellent lithium-storage performance including high reversible capacity,good cycling durability and high-rate capability.Whereas the electrode with the polyvinylidene fluoride（PVDF）binder suffered from rapid capacity decay under the same test conditions.As a result,the NiFe₂O₄/rGO composites with CMC binder electrode in this work are promising as anodes for high-performance LIBs,resulting from the synergistic effect of optimal graphene content and proper choice of binder.Transition metal sulfides not only have the advantages of oxides,but also hold better conductivity and smaller volume change.Among these transition metal sulfides,cobalt sulfides with abundant reserves have high specific capacity and good conductivity.However,it shows larger volume changes during charge-discharge process.This leads to the pulverization of the electrode materials and that even causes the electrode materials to fall off the base.The above problems can be solved by optimizing the material structure and using carbon composite.According to the characteristics of cobalt sulfide materials,we have obtained specific morphologies and sizes of transition metal sulfides and their carbon composites by the simple solvothermal methods and the metal-organic frameworks template methods.We use it as the electrode material for lithium ion battery,and systematically discuss and study its electrochemical performance.更多还原